Overload shunt with single resistor element

ABSTRACT

An overload shunt includes at least one resistor element having a nonlinear resistance and comprising material compressed from at least two directions toward each other. The resistor element has a width formed in the directions of compression and a length parallel to its longitudinal axis and perpendicular to the directions of compression. The length is at least as great as the width. The resistor element is positioned in a manner whereby current in the overload shunt flows along the length of the resistor element perpendicularly to the directions of compression.

United States Patent Inventors Rudoll Foitzik;

Klaus Reichelt, both of Berlin, Germany Appl. No. 878,863

Filed Nov. 21, 1969 Patented June 22, 1971 Assignee SiemensAktleugesellschalt Berlin, Germany Priority Nov. 26, 1968 Germany P 1812253.7

OVERLOAD SHUNT WITH SINGLE RESISTOR ELEMENT 10 Claims, 11 Drawing Figs.

US. Cl 317/68, 29/615, 338/223 Int. Cl 1102b 1/04, H01c 15/04 Field ofSearch 252/504;

[56] References Cited UNlTED STATES PATENTS 2,305,577 12/1942Stoelting... 254/61 (X) 2,331,852 10/1943 Stoelting 338/223 (X)2,376,815 5/1945 Roman 264/104 (X) 3091,72] 5/1963 Yost 317/68 (X)Primary Examiner-.1. D. Miller Assistant Examiner-Harvey FendelmanAtromeysCurt M. Avery, Arthur E. Wilfond, Herbert L.

Lerner and Daniel]. Tick ABSTRACT: An overload shunt includes at leastone resistor element having a nonlinear resistance and comprisingmaterial compressed from at least two directions toward each other. Theresistor element has a width formed in the directions of compression anda length parallel to its longitudinal axis and perpendicular to thedirections of compression. The length is at least as great as the width.The resistor element is positioned in a manner whereby current in theoverload shunt flows along the length of the resistor elementperpendicularly to the directions of compression.

PATENT ED- JUN 2 2 Ian SHEET 3 OF 3 OVERLOAD SHUNT WITH SINGLE RESISTORELEMENT DESCRIPTION OF THE INVENTION The invention relates to anoverload shunt. More particularly, the invention relates to an overloadshunt with a single resistor element.

An overload shunt or surge voltage arrestor of known type includes aplurality of resistor elements. Each of the resistor elements comprisessilicon carbide with added compounds. The resistor element may beproduced by compressing 70 percent80 percent silicon carbide powder witha porcelain compound, for example. The compressed material is then bakedfor about 1300 C. Other types of resistor elements may be produced bythe addition of a mixture of clay, prepared chalk and water glass as abanding material. The compressed material is then hardened at about220500C.

Prior to our invention, resistor elements were provided in the shape ofdiscs having axial lengths which were less than their. diameters.'During the manufacture of such discs, the material comprising the discswas compressed in axial direction. The discs are usually provided with ametal contact layer on their surfaces. The contact layer may beprovided, for example, by a layer of copper which is sprayed on. Inoperation of the surge voltage shunt, the resistor discs areelectrically charged by the voltage drop and the current which flows inthe same direction as the axis of the disc. The current flow is thus inthe directions of compression of the disc resistor element.

It has been shown that the axial length cannot be selected arbitrarilyrelative to'the diameter of the disc resistor element. A quadraticprofile, of the axial length and diameter, is impractical. Such discsusually break down soon after the flow of surge current through them andupon'the application of long waves thereto. They are therefore notutilizable for practical applications. This may be due to theinhomogeneity of the disc, especially along its edges. Suchinhomogeneity is caused by the considerable friction which occursbetween the surfaces of the disc and the die during compression. Thefriction increases with increased axial length of the disc. For thisreason, a plurality of relatively flat disc resistor elements have beenutilized as the nonlinear resistor element of an overload shunt formedium and high voltages.

The principal object of the invention is to provide a new and improvedresistor element for an overload shunt.

An object of the invention is to provide a new and improved overloadshunt.

An object of the invention is to provide a resistor element whichovercomes the disadvantages of known resistor elements.

An object of the invention is to provide a resistor element which has awidth which is small relative to its axial length and is thereforehomogenous.

An object of the invention is to provide a resistor element which has anaxial length which is 2 to 4 times greater than its width.

An object of the invention is to provide an overload shunt in which asingle resistor element of elongated configuration replaces a pluralityof disc resistor elements.

An object of the invention is to provide an overload shunt which isinexpensive to manufacture due to the fewer number of resistor elementsincluded therein.

In accordance with the invention, an overload shunt includes at leastone resistor element having a nonlinear resistance and comprisingmaterial compressed from at least two directions toward each other. Theresistor element has a width formed in the directions of compression anda length parallel to its longitudinal axis and perpendicular to thedirections of compression. The length is at least as great as the width.Positioning means positions the resistor element in a manner wherebycurrent in the overload shunt flows along the length of the resistorelement perpendicularly to the directions of compression.

The resistor element may have a rectangular cross-sectional area, or aprismatic cross-sectional area, or a circular crosssectional area, orother geometrical cross-sectional area. The positioning means comprisesa tubular member coaxially surrounding the resistor element andcomprising electrically insulating material.

At least two resistor elements are provided, coaxially positioned one oneither side of spark gap means. A first plurality of resistor elementsare positioned on one side of the spark gap means and a second pluralityof the resistor elements are positioned coaxially with the-firstplurality of resistor elements on the other side of the spark gap means.

A tubular member of electrically insulating material is coaxiallypositioned around the first and second pluralities of resistor elementsand the spark gap means. The resistor elements of the first plurality ofresistor elements are electrically connected in parallel with each otherand the resistor elements of the second plurality of resistor elementsare electrically connected in parallel with each other.

Prior to our invention, the resistor elements have been utilized only inseries arrangement, since a parallel arrangement of disc resistorelements tends to be unstable due to the negative temperaturecoefficient thereof. It has therefore beennecessary to manufacture discresistor elements of various 1 types and sizes for overload shunts ofdifferent values. The resistor element of our invention is electricallycharged perpendicularly to the directions of compression and has aconsiderably higher specific energy capacity than the resistor elementdiscs of the prior art. The resistor elements of our invention maytherefore be arranged in parallel with each other, without difficulty.It is therefore possible to manufacture only one type of resistorelement for a relatively small electrical charge and stock it for theoverload shunts rated for higher charges by utilizing two or more ofsuch resistor elements, electrically connected in parallel, in anoverload shunt.

The resistor element of the present invention having a prismaticcross-sectional area isyof substantially square crosssectional areahaving a slight taper. Such a resistor element has an additionaladvantage that it may be centered in a simple manner along its edges bythe surrounding tube of electrically insulating material.

In order that the invention may be readily carried into effect, it willnow be described with reference to the accompanying drawings, wherein:

FIG. I is an axial sectional view of an embodiment of the overload shuntof the invention;

FIG. 2 is a cross-sectional view, taken along the lines II-II of FIG. 1;

FIG. 3 is a longitudinal sectional view, taken along the lines III-IIIof FIG. 4, of a compression die utilized to manufacture a resistorelement of the invention having a square cross-sectional area; 1

FIG. 4 is a top view of the die of FIG. 3;

FIG. 5 is a cross-sectional view, taken along the lines V-V of FIG. 4,of the compression die of FIG. 4;

' FIG. 6 is a cross-sectional view of a compression die formanufacturing a resistor element of the invention having a prismaticcross-sectional area;

FIG. 7 is a cross-sectional view of a compression die for manufacturinga resistor element of the invention having a circular or ovalcrosssectional area;

FIG. 8 is a cross-sectional view of a compression die for manufacturinga resistor element of the invention having an octagonal cross-sectionalarea;

FIG. 9 is a cross-sectional view of a compression die for manufacturinga resistor element of the invention having a hexagonal cross-sectionalarea;

FIG. 10 is an axial sectional view of another embodiment of the overloadshunt of the invention; and

FIG. 11 is a cross-sectional view, taken along the lines Xl-XI of FIG.10.

In FIG. 1, an outer ribbed housing 1 comprises electrically insulatingmaterial such as, for example, porcelain. The insulating housing 1 is ofgenerally hollow cylindrical configuration and is closed at its top baseby a metal cap 2 via a sealing gasket 3 which is cemented to saidhousing by any suitable adhesive such as, for example, cement 4. Theinsulating housing 1 is closed at its bottom base by a metal cap 5 and asealing gasket 6.

A deflection disc 7 coaxially surrounds the bottom metal cap 5'of theinsulating housing 1 and is affixed to a diaphragm 8, which isinterposed between said cap and said disc. The deflection disc 7supports a ground wire or cable 9. Upon the failure of the overloadshunt, the diaphragm 8 is destroyed by the resulting high pressure andthe deflection disc 7 and the ground wire 9 are thrown off.

The overload shunt includes a stack 10 of spark gaps, coaxiallypositioned in the insulating housing 1, as shown in FIG. 1. The stack 10of spark gaps is coaxially positioned in an annular or hollowcylindrical control resistor 11. A first resistor element 12, of squarecross-sectional area, is positioned in the insulating housing 1 abovethe stack 10 of spark gaps. A second resistor element 12', of squarecross-sectional area, is positioned below the stack 10 of spark gaps.

The first resistor element 12 has an electrically conductive metal layeron its top surface 12a and an electrically conductive metal layer on itsbottom surface 12a in order to improve its electrical connection withthe other elements of the overload shunt. The metal layers on the topand bottom surfaces may comprise copper which may be sprayed on. Thesecond resistor element 12 is provided with top and bottom electricallyconductive metal layers, not shown in FIG. 1.

A top metal spacer 13 is coaxially positioned in the insulating housing1 in electrical contact with the top surface metal coating 12a of thefirst resistor element 12. A bottom metal spacer 14 is coaxiallypositioned in the insulating housing 1 in electrical contact with thebottom surface metal layer of the second resistor element 12'. Thecomponents in the housing 1 are supported by a base member 15 whichrests upon the diaphragm 8. The components of the overload shunt arecoax ially positioned in a tubular member 16 of electrically insulatingmaterial. The tubular member 16 is coaxially positioned in theelectrically insulating housing 1. The tubular member 16 may comprise,for example, stiff paper. As shown in FIG. 2, the longitudinal edges ofthe second resistor element 12, and, as not shown in the. F 105., thelongitudinal edges of the first resistor element 12, abut against theinside surface of the tubular member 16. Air spaces 17 (FIGS. 1 and 2)between the resistor elements 12 and 12' and the tube member 16 functionto equalize pressure, especially during an overload.

In FIG. 1, the directions of compression, in which the materials of theresistor elements 12 and 12' are compressed, are indicated by arrows 18and 18. The direction of the electrical charge, which is also thedirection of operating current flow, is indicated by an arrow 19. Theaxial length of each of the resistor elements 12 and 12, which is thelength in the direction of arrows 19, is at least as great as the widthof said resistor elements, in the directions of compression. In FIG. 1,the axial length of each of the resistor elements 12 and 12' is severaltimes greater than the width thereof in the directions of compression,and is approximately 2 5; times as great.

FIGS. 3, 4 and 5 show a compression die for producing resistor elementsof the invention having a square cross-sectional area. As shown in FIGS.3, 4 and 5, the compression die comprises a massive frame 20a, 20bhaving an opening 21 formed therein. A pair of compression pistons 22and 23 are positioned in the opening 21 of the die 20a, 20b in a mannerwhereby they are movable relative to each other and toward each other.The material 24, of silicon carbide and a binding agent, to becompressed, is placed in the opening 21. The compressing force isapplied in the direction of arrows and 25 and may comprise about 100 to1000 kp per cm?, and is preferably 750 kp per cm.

As shown in FIGS. 3, 4 and 5, the compression forces are perpendicularto the axial or longitudinal direction of the material 24 to becompressed, so that the compression pistons 22 and 23 move only a smalldistance. In this manner, inhomogeneity of the compressed material, dueto friction, is prevented to a large extent. In use in the overloadshunt, the resistor element comprising the compressed material 24 iselectrically charged along its longitudinal or axial length, as shown inFIG. 1.

The compression die, as shown in FIG. 6, may be formed so that thecompressed material 24 has a slightly tapered, essentially rectangular,cross-sectional area. The cross-sectional area of the resistor elementis thus substantially prismatic and is removable from the compressiondie with considerable facility. 7

FIG. 7 illustrates a compression die for manufacturing a resistorelement 24 having a circular or oval cross-sectional area. FIG. 8illustrates a compression die for manufacturing a resistor element 24"having an octagonal cross-sectional area. FIG. 9 illustrates acompression die for manufacturing a resistor element 24"" having ahexagonal cross-sectional area. Each of the compression dies of FIGS. 6,7, 8 and 9, as the compression die of FIGS. 3, 4 and 5, produces acompressed material resistor element having a longitudinal or axiallength which is greater than its width in the directions of compression.

The embodiment of the overload shunt of FIGS. 10 and 11 is generallysimilar to that of FIGS. 1 and 2. The overload shunt of FIGS. 10 and 11includes a stack 30 of spark gaps.

Eight resistor elements 31a, 31b, 31c, 31d, 31e, 31f, 31g and 31h of theinvention, as hereinbefore described, are included in the overloadshunt. Each of the resistor elements 31a to 31h is identical with theresistor element 12 or 12 of the embodiment of FIGS. 1 and 2.

Four resistor elements 31a, 31b, 31c and 31f are positioned in thetubular member 34, in the insulating housing, above the stack 30 ofspark gaps. The resistor elements 31a, 31b, 31c and 31f are electricallyconnected to each other in parallel and are commonly electricallyconnected by an electrically conductive metal plate 32 covering thebottom surfaces thereof. The metal plate 32 electrically contacts thetop of the stack 30 of spark gaps. The four resistor elements 31a, 31b,31c and 31f are positioned by the tubular member 34.

Four resistor elements 31c, 31d, 31g and 31h are positioned in thetubular member 34, in the insulating housing, below the stack 30 ofspark gaps. The resistor elements 31c, 31d, 31g and 31h are electricallyconnected to each other in parallel and commonly electrically connectedby an electrically conductive metal plate 33 covering the top surfacesthereof. The metal plate 33 electrically contacts the bottom of thestack 30 of spark gaps. The four resistorelements 31c, 31d, 31g and 31hare positioned by the tubular member 34.

While the invention has been described by means of specific examples andin specific embodiments, we do not wish to be limited thereto, forobvious modifications will occur to those skilled in the art withoutdeparting from the spirit and scope of the invention.

We claim:

1. An overload shunt including:

at least one resistor element having a nonlinear resistance andcomprising material compressed at least two directions toward eachother, said resistor element having a width formed in the directions ofcompression and a length parallel to its longitudinal axis andperpendicular to the directions of compression, said length being atleast as great as said width; and

positioning means positioning said resistor element in a manner wherebycurrent in said overload shunt flows along the length of the resistorelement perpendicularly to said directions of compression.

2. An overload shunt as claimed in claim 1, wherein the length of theresistor element is several times greater than its width in thedirections of compression.

3. An overload shunt as claimed in claim 2, wherein said resistorelement has a rectangular cross-sectional area.

4. An overload shunt as claimed in claim 2, wherein said resistorelement has a prismatic cross-sectional area.

5. An overload shunt as claimed in claim 2, wherein said resistorelement has a circular cross-sectional area.

6. An overload shunt as claimed in claim 2, wherein said positioningmeans comprises a tubular member coaxially surrounding said resistorelements, said tubular member comprising electrically insulatingmaterial.

7. An overload shunt as claimed in claim 2, further comprising spark gapmeans and at least two of said resistor elements coaxially positionedone on either side of the spark gap means.

8. An overload shunt as claimed in claim 2, further comprising spark gapmeans and a plurality of said resistor elements, a first plurality ofsaid resistor elements being positioned on one side of said spark gapmeans and a second plurality of said resistor elements being positionedcoaxially with said first plu- -rality of resistor elements on the otherside of said spark gap

1. An overload shunt including: at least one resistor element having anonlinear resistance and comprising material compressed at least twodirections toward each other, said resistor element having a widthformed in the directions of compression and a length parallel to itslongitudinal axis and perpendicular to the directions of compression,said length being at least as great as said width; and positioning meanspositioning said resistor element in a manner whereby current in saidoverload shunt flows along the length of the resistor elementperpendicularly to said directions of compression.
 2. An overload shuntas claimed in claim 1, wherein the length of the resistor element isseveral times greater than its width in the directions of compression.3. An overload shunt as claimed in claim 2, wherein said resistorelement has a rectangular cross-sectional area.
 4. An overload shunt asclaimed in claim 2, wherein said resistor element has a prismaticcross-sectional area.
 5. An overload shunt as claimed in claim 2,wherein said resistor element has a circular cross-sectional area.
 6. Anoverload shunt as claimed in claim 2, wherein said positioning meanscomprises a tubular member coaxially surrounding said resistor elements,said tubular member comprising electrically insulating material.
 7. Anoverload shunt as claimed in claim 2, further comprising spark gap meansand at least two of said resistor elements coaxially positioned one oneither side of the spark gap means.
 8. An overload shunt as claimed inclaim 2, further comprising spark gap means and a plurality of saidresistor elements, a first plurality of said resistor elements beingpositioned on one side of said spark gap means and a second plurality ofsaid resistor elements being positioned coaxially with said firstplurality of resistor elements on the other side of said spark gapmeans.
 9. An overload shunt as claimed in claim 8, further comprising atubular member coaxially positioned around said first and secondpluralities of resistor elements and said spark gap means, said tubularmember comprising electrically insulating material.
 10. An overloadshunt as claimed in claim 9, wherein the resistor elements of said firstplurality of resistor elements are electrically connected in parallelwith each other and the resistor elements of said second plurality ofresistor elements are electrically connected in parallel with eachother.